This invention relates to a method of making an .alpha.-chloro-.alpha.,.alpha.-difluoro aromatic compound, such as .alpha.-chloro-.alpha.,.alpha.-difluoro-toluene, .alpha.,.alpha.'-dichloro-.alpha.,.alpha.,.alpha.',.alpha.'-tetrafluoro-p- xylene (DCTFPX), .alpha.,.alpha.'-dichloro-.alpha.,.alpha.,.alpha.',.alpha.'-tetrafluoro-m- xylene (DCTFMX), .alpha.,.alpha.',.alpha."-trichloro-.alpha.,.alpha.,.alpha.',.alpha.',.alp ha.,.alpha."-hexafluoro-mesitylene, and .alpha.-chloro-.alpha.,.alpha.-difluoro-naphthalene. In particular, it relates to the reaction of an .alpha.,.alpha.,.alpha.-trichloro aromatic compound with hydrogen fluoride (HF) in the presence of a catalyst to produce the corresponding .alpha.-chloro-.alpha.,.alpha.-difluoro compound.
DCTFPX is a precursor for an inter-layer dielectric material used for making semiconductor chips; it is also a precursor for inert and transparent conformal coatings for electrical components. It has been made by reacting the corresponding dialdehyde with SF.sub.4 followed by side-chain chlorination. See "The Synthesis of 1,1,2,2,9,9,10,10-Octafluoro-[2.2]paracyclophane" by S. W. Chow et al., The Journal of Organic Chemistry, vol. 35, pages 20-22 (1970), "The Chemistry of Sulfur Tetrafluoride. II. The Fluorination of Organic Carbonyl Compounds," by W. R. Hasek et al., J. Amer. Chem. Soc.; vol. 82, pages 543-551 (1960), and "Synthesis and Chemistry of Several Fluorinated p-Xylenes Designed as Precursors for .alpha.,.alpha.,.alpha.',.alpha.'-Tetrafluoro-p-Xylene," by S. A. Fuqua et al., Tetrahedron, vol. 20, pages 1625-1632, (1964).